According to experiences, zones of weaknesses, joint systems and sliding surfaces in rock masses, have a great effect on the deformation behavior of tunnel cross section and the stress development in the shotcrete cover. The loosening and detaching of rock due to roof deformations in turn can take progressive dimensions and lead to roof fall and in extreme case cave to the surface.
In this study, the effect of weakness zones on increasing roof deformations is demonstrated and the radius of influence of such weaknesses is determined using a FE- program for 3- dimensional continuum. Furthermore it is shown that the thickness of such disturbances does not significantly affect the development of deformations i.e. if the stiffness conditions remain constant. Also the viscous material causes greater deformations than the elastic one. Finally the study indicates that
tangential stresses in the lining are also increased by weakness zones.